Taking the chronology of his works that I linked above, a small amount of data-cleansing (whenever the date was spread over two years, took the latter e.g. 1885-86 becomes 1886), and some basic annotation I got to this timeline graph (click to enlarge).

Exactly what it was that was driving him is unclear to this day. One of the leading theories is bi-polar disorder which would explain the periods of manic activity followed by deep dispare. I was discussing this recently with a friend who is a lecturer in psychology who said that the manic phases were exceptionally long and intense.

What is amazing is the result. In Arles (February 1888 – May 1889) he created over 200 pieces in 15 months of which he sold none. He was commited / committed himself to a mental institution at St Rémy in May 1889. While in the hospital he did another 150 paintings over the course of a year. After leaving the hospital in May 1890 he went on to create another 70 paintings in as many days before killing himself in July 1890. What I was surprised to see was that back in 1885 he painted over 140 paintings, before moving to Paris. This is when he did some of his famous “dark” paintings of peasant life like the The Potato Eaters.